Cleaned up RobotBase, removed singleton list from SensorBase, and removed unused typedefs and NULL_TASK macro from HAL's Task.hpp. Making the robot class instance static fixed non-POD statics used by the instance during destruction from being destroyed first.
Rename the following folders:
hal/lib/Athena -> hal/lib/athena
hal/lib/Desktop -> hal/lib/sim
hal/lib/Shared -> hal/lib/shared
wpilibc/Athena -> wpilibc/athena
wpilibc/simulation -> wpilibc/sim
Windows users may need to run gradlew clean after updating.
